The present invention is directed to flat roofing systems, and more particularly to a ventilating system for such roof systems. The primary components of a flat roof system are the roofing cover or membrane, the insulation layer, and the supporting deck. Various approaches have been taken to prevent leakage in these types of roofing systems, but little or nothing has been designed to remove or dissipate moisture which does happen to accumulate in the insulation layer of the roof.
It is relatively easy to ventilate a cold attic below a gabled residential roof because a large air space (i.e., the attic) is available. See U.S. Pat. Nos. 3,797,180 and 3,972,164. However, in compact roofs such as the built-up or flat-roof type, ventilation becomes far more difficult because little or no air space exists between the components. In most of these compact systems the roofing membrane is of a multi-layer type broadly including of a layer of insulating felt over a support deck, a layer of hot bituminous adhesive material mopped over the felt, and an aggregate material forming the exterior surface of the roof. An additional vapor barrier such as a layer of polyethylene may or may not be included between the felt and the underlying support deck. The vapor barrier inhibits the flow of vapor or moisture through the roofing system. For most buildings that are potentially problematic, vapor or moisture that enters a roof during the cold season is less of a problem when there is ample opportunity during the summer season to dry out.
In textile mills, carpet mills, and other highly humid facilities, however, the summer drying period may not be sufficient to overcome vapor accumulation in the roofing insulation. In the past, such humid facilities have been provided with highly efficient vapor barriers or retarders and/or supplementary venting devices. The venting devices do not provide for removal of accumulated moisture, but such provisions do improve air flow through the roof and help keep the insulation dry if the vapor retarder is adequate for the given conditions.
Where the ventilation and vapor retarding measures are insufficient to control the moisture problem and prevent moisture accumulation in the insulation layer, it is usually necessary to eventually strip away and replace the wet insulation and the roofing material in the damaged area. This is obviously an expensive procedure and to be avoided where possible.
Additionally, damage and destruction of roofing systems caused by fire have in the past been resolved by replacement of the damaged roof. Fire damage to the roof during the fighting of a fire can occur in at least two ways, and carpet and textile mills are among the most susceptible of facilities. The first way, of course, is the outbreak of fire followed by soaking of the roofing and insulation to extinguish or inhibit spread of the fire. A second common cause of damage is cutting or breaking of the roofing structure by firemen to control the fire. Where the roof is not burned or broken into, the roof system of the present invention becomes extremely important.
The minimizing of problems in moisture accumulation and the improvement of fire control in roofing structures are the problems confronted by the present invention.
Broadly described, the improved roofing system comprises a compact flat-roof system including a grid-type ventilation structure or means intermediate the supporting deck and the overlying insulation and composition membrane. The ventilation means provides for the movement of air between the layers of the roof structure and includes a grid member molded or otherwise formed from a plastic or metallic material.
The grid member is in the form of a planar configuration having a plurality of relatively large openings formed through the thickness thereof. The grid is supported on piers or legs atop the underlying supporting deck to provide for movement of air or vapor between the layers of the roofing structure. The grid sheets are provided in a variety of sizes from approximately 3'.times.8' to 9'.times.20', and of a thickness from 1" to 4" from bottom of foot to top of plate.
The grid member is supported on its legs or piers on the conventionally prepared deck and the sheets of insulation are placed thereover, followed by construction of the composition membrane. Thus positioned in the roofing structure, the grid member provides a substantially improved means for permitting air to flow through the roofing structure, thus improving the control of moisture accumulation in the insulation and roofing structure as a whole.
A further modification of the system includes the provision of a plurality of spaced apart, vertically extending vents or conduits opening to the exterior surface of the roof from a selected area of the grid ventilating means. These conduits, or vents, function as inlets or outlets for pumping water into the roofing system for fire extinguishing, or vacuuming accumulated water out of the roofing system to facilitate the drying of the insulation.
Other advantages to the use of the improved roofing system include: (1) roofing insulation is separated and isolated from water that enters the structure when the roofing membrane leaks; and (2) the air space gained through use of the grid member acts as additional thermal insulation. It is anticipated that other and further modifications will become apparent to those skilled in the art as the following detailed description is studied in conjunction with accompanying drawings, in which: